The Machinery and Mechanism of Multidrug Efflux in Gram-negative Bacteria
Dijun Du, Henrietta Venter, Klaas M. Pos and Ben F. Luisi
from: Microbial Efflux Pumps: Current Research (Edited by: Edward W. Yu, Qijing Zhang and Melissa H. Brown). Caister Academic Press, U.K. (2013)
Abstract
The Gram-negative bacteria are enveloped with a protective double-layer of lipid membranes, across which they expel noxious compounds by active transmembrane transport. Several classes of membrane-spanning proteins mediate the transport and thereby confer the bacteria with the capacity to occupy hazardous ecological niches or to evade the cytotoxic effects of antimicrobial compounds. The proteins can be grouped into diverse structural families, but all drive transport uphill energetically, against concentration gradients, using the free energy of electrochemical gradient or of ATP hydrolysis. One group of trans-membrane proteins forms an assembly that spans the inner and outer membranes and the periplasm. The inner membrane component of the assembly recognizes substrates for transport and harnesses energy for the processes, whereas a major role of the periplasmic adapter is to connect the inner membrane component to the outer membrane channel to safeguard the transport of the captured substrate across the outer membrane. The outer membrane component has an adjustable aperture that may be opened through interaction with its partner pump proteins. Using the AcrA/AcrB/TolC assembly of Escherichia coli as a paradigm efflux machine, we describe the current knowledge of the pump components and speculate on how they might interact in an allosteric manner during the transport process read more ...
